The invention relates generally to freight train brake control systems and more particularly to a system for operably interfacing ECP equipped freight cars with non-ECP equipped locomotives.
The North American Railroad industry, lead by the Association of American Railroads (AAR) has developed standards for Electrically Controlled Pneumatic (ECP) brakes. These standards include an electric trainline, 2 wire, 8 gauge, which operates at 230 VDC, for providing power and communications to and from the ECP units on each car. Communications must following Echelon LonWorks standards, using a PLT-10A transceiver. Each car is budgeted at up to 10 watts power consumption, in a train of 160 cars, up to 12,000 ft. length. A separate 230 VDC cable must be provided through each locomotive and a 230 VDC locomotive power supply rated at 2,500 watts is required on at least one of the locomotives to power the ECP system on each car. Additionally, a locomotive ECP "head end unit" (HEU) is required to provide communications, locomotive interfaces, and operator interface with the ECP cars.
The ECP system may be provided as overlay to conventional pneumatic brake valves, or as "all electric," replacing the pneumatics service portion function. The "all electric" ECP system provides the most economical solution, but requires locomotives to be equipped to support ECP operation. There are usually multiple locomotives for a train, and all are required to be equipped with the 230 VDC ECP trainline cable. The lead locomotive must have the ECP HEU and at least one locomotive has to be equipped with the 230 VDC ECP power supply.
Prior art ECP systems which are of the "overlay" type permit the cars to be operated in normal pneumatics mode braking ECP when ECP equipped locomotives were not available. Additionally, even with "all electric" ECP cars, a "pneumatic emulation" mode can be provided using the ECP system battery or an on-board power source. Pneumatic emulation describes the operation of the ECP system when braking commands are communicated to the ECP equipment pneumatically via the brake pipe in the same manner as conventional pneumatic operation, rather than by an electric command signal. Thus, a non-ECP locomotive can still operate the brakes on ECP cars. The downside of the emulation mode described is that the power source for the ECP system is problematic. If an ECP battery is used there will necessarily be a limited operating life. The alternative, adding on-board power generation, greatly adds to the cost of the system.
In any event, future ECP trains designed to AAR guidelines, with the separate 230 VDC trainline, require each car and all locomotives in the train to be modified. With the exception of small "captive" railroads which do not need to interchange cars and locomotives with others, it is very difficult to manage the transition to full ECP operation. Therefore, each car would have to be equipped to operate with both ECP and conventional pneumatic brake systems. However, for many companies it is not economically viable to equip each car with both ECP equipment and pneumatic control valves. Likewise, it is an economic penalty to require on -board power generation to support electric emulation for conventional pneumatics operation.
Therefore, there is a need for a way to employ ECP cars with non-ECP locomotives without having to rely on the ECP battery or requiring on-board power generation. Accordingly, an apparatus and method is provided for operating the ECP equipment on-board each car in a low power emulation mode which can be powered indefinitely by the standard 74 VDC locomotive battery. Consequently, "all electric" ECP cars can be powered and controlled by standard, unmodified locomotives thereby supporting a gradual transition to "all electric" ECP cars without the need to retrofit every locomotive within a short time period. Additionally, co-pending U.S. patent applications Ser. No. 09/224,543, titled "ECP TRAIN LINE COMMUNICATIONS FOR RAILWAY FREIGHT CAR BRAKES," filed Dec. 31, 1998, and Ser. No. 09/224,541, titled "RAILWAY LOCOMOTIVE ECP TRAIN LINE CONTROL," filed on Dec. 31, 1998, which similarly disclose subject matter related to the transition from pneumatic to ECP brake systems, are hereby incorporated herein by reference.